Patent GB-877837-A (GB)
Title: Improvements in power plants
IPC: F22B1/08
Filed: 1959-05-28
Abstract: 877,837. Generating combustion products under pressure. FOSTER WHEELER Ltd. May 28, 1959 [May 28, 1958], No. 18292/59. Class 51 (1). [Also in Groups XIII and XXVI] A combined gas and steam cycle power plant comprises two pressure-fired steam generators, one of which includes a convectively heated first-stage superheater and a convectively heated steam re-heater in addition to steam generating tubes, and the other of which includes a convectively-heated second stage superheater in addition to steam generator tubes; a gas-turbine connected to receive hot combustion gases from the steam generators and drivingly connected to an air compressor for the supply of combustion air to the steam generators, also to a useful power machine; a multi-stage steam turbine set connected to receive superheated steam from the second stage superheater and to return steam to the reheater to be re-heated between two of its stages; and an after-burner or reheater disposed in the duct through which combustion gases flow to the gas turbine, whereby the temperature of these gases can be maintained at or near a prescribed maximum value for optimum efficiency. The plant shown comprises a pair of pressure-fired steam generators 11, 12 which supply superheated steam to a steam turbine set, not shown, steam from an intermediate stage being re-heated in a reheater in steam generator 11. Combustion gases from the combustion chambers of the steam generators 11, 12 discharge through duct 15 and drive a gas turbine 91 which drives an air compressor 92 and an electric generator 93, air from the compressor passing through ducts 34, 34A to the combustion chambers of the steam generators. An after-burner 90 is disposed in the combustion gas duct 15 and fuel may be supplied thereto, also air tapped from the ducts 34, 34A through ducts 95, 96, and 98; some air may also be led into the duct 15 upstream of the after-burner 90 through duct 97. The steam generators 11, 12 are mounted vertically sideby-side with the combustion gas outlet duct 15 disposed vertically between them. The steam generator 11 comprises a cylindrical shell 17 and a refractory lining 16 within which is a lower radiant furnace section 25 and an upper convection section 26. Air under pressure, for example 75 lb. per square inch gauge, supplied through duct 34 enters the chamber 31 from which it issues through openings 32 and through openings 28 in the wall 27 into the combustion chamber 25. Fuel is supplied to the latter through burners 29. The wall of the combustion chamber 25 is lined with axiallyextending tubes 35 which extend between an inlet header 36 and an outlet header 37, the inlet header being connected to the common steam and water drum 13 by way of a pair of downcomers 38 and distribution pipes 39 and the outlet header being connected to the steam and water drum by way of riser pipes 40. The upper part of the combustion chamber is formed of rectangular cross-section by means of walls 41, 42, 43, 44, a combustion gas outlet duct 46 extending through wall 41. The walls are lined with axially-extending steam generator tubes 48, 49, 50, 51 respectively, the tubes extending between inlet and outlet headers 52 and 53, 54 and 55, 57 and 59, 58 and 60 respectively. The inlet headers 52, 54, 57 and 58 are connected to the steam and water drum 13 by way of pipes 61 from the downcomers 38, and the outlet headers 53, 55, 59 and 60 are connected to the steam and water drum by way of pipes 62. Steam from the drum 13 passes to the inlet header 70 of the first stage superheater 64 by way of pipe 72, the inlet header being connected to the outlet header 71 by way of tubes 69 which have horizontallyextending portions connected by reverse-flow bends. A convectively-heated steam reheater 63 is also disposed at the upper part 45 of the steam generator 11 and comprises an inlet header 67 to which steam from an intermediate turbine stage is passed through inlet pipe 68, the inlet header 67 being connected to the outlet header 66 by way of tubes 65 which have horizontally-extending portions connected by reverse-flow bends. Re-heated steam is returned to the turbine from outlet header 66 by way of pipe 74. The tubes of the first stage superheater and the reheater are arranged so that either may be removed without interfering with the other, the upper portion 23 of the combustion chamber shell having a removable cover and being large enough to permit their removal. Steam from the first stage superheater 64 passes from outlet header 71 through pipe 73 having an expansion bend 77 to the inlet header 75 of the second stage superheater 76 which is disposed at the upper part 45A of the steam generator 12 and comprises a series of horizontally-extending tubes 81 connected by reverse-flow bends extending between inlet header 75 and outlet header 82, steam passing from header 82 to the turbine inlet through duct 84. The steam generator 12 is similar to generator 11 except that the convectively-heated second stage superheater 76 only is provided in the upper part 45A, no reheater being provided therein. Combustion gases from the steam generators discharge through outlets 46, 83 to a common pipe 15 through which gases pass to the inlet of the gasturbine 91 finally discharging through a feed water heater to atmosphere. The air compressor 92 driven by the turbine 91 supplies air under pressure through ducts 34, 34A to the combustion chambers of the steam generators 11, 12 under control of valves 103. Air may also be fed from the ducts 34, 34A through ducts 95, 96 and 98 to a reheat chamber 90 disposed in the combustion gas duct 15, the air supply being controlled by valve 100. Fuel is also supplied to the reheater chamber through a burner not shown. Air from the duct 97 may be supplied into the exhaust gas duct 15 upstream of the reheat chamber 90 under control of valve 99. A control device sensitive to pressures at the gas-turbine inlet and compressor outlet is provided to control the valve 99.